Fish Intake and Mercury
Fish has long been a part of athletic and other ‘healthy’ diets and there are many many reasons for that to be the case. In no particular order, here are a few:
Fish is a high-quality animal protein which is generally readily available and (depending on location) fairly inexpensive. As well, low-fat fish (canned tuna has been a stable for athletes and bodybuilders for decades) are nearly fat free and, as it turns out, even the fattier cuts of fish contain a large amount of ‘healthy’ fats in the form of the omega- 3 fish oils.
As I mentioned in What are Good Sources of Protein – Amino Acid Profile Part 1, some work has also suggested that the high taurine content of fish may improve insulin and/or leptin sensitivity.
All of these factors add up to fish being a good choice of proteins.
However, at the same time, not all is good in the land of fish. An issue of some concern has to do with the mercury content of fish. Mercury, as I imagine most know, is a toxic metal compound that, when it accumulates in the body, can cause a lot of problems.
A question that comes up often enough to be worth addressing is just how much fish can be consumed on a daily basis to get the benefits of it as a protein source while avoiding potential issues with mercury.
To address this, I’m simply going to excerpt the section on fish from Chapter 10: Whole Food Protein of The Protein Book where I examine fish protein and the issue of mercury content.
As you’ll see, depending on the type of fish in question, mercury can range from non-detectable to very low to exceedingly high. And given the recommendations (at the end of the article) for daily limits to mercury content, it becomes clear that while some fish can be consumed in significant amounts daily, others are limited (e.g. 4-5 oz of canned tuna per day is about the limit even if bodybuilders and athletes often eat far more than that) and others exceed daily intake recommendations by far.
Fish is a high quality protein and many types of fish are extremely low fat, making it an excellent protein source choice. There are numerous varieties of fish and, similar to fowl, fish is appropriate at all times of the day except immediately around training. Of interest to dieting athletes, some research has found that fish keeps people fuller compared to either chicken or red meat (1).
Although fish is often chosen for its low-fat content, even the higher fat (typically cold water) fish typically contain most of their fat in the form of the omega-3 fish (w-3) oils. These fats have a tremendous number of benefits, both for general health and athletic performance.
The beneficial effects of fish oils are numerous and include increased fat burning, decreased fat storage, decreased inflammation, decreased depression, mood stabilization, and decreased risk of heart disease and blood clots. More benefits are being found constantly and it’s not an exaggeration to say that, if individuals were to take any single supplement on a daily basis, it should be a fish oil supplement. Although food scientists are working to increase the w-3 content of other foods (such as w-3 eggs described below), fatty fish remain the primary source in the food supply.
However, counteracting the potential benefits of fish and the w-3 fatty acids, there is increasing concern over the mercury content of many types of fish; because of their place in the food chain, mercury accumulates in the tissue of the fish to varying degrees.
Chronic mercury exposure could potentially offset the benefits that fish might provide (1). Because of the potential health effects of mercury, both the United States Environmental Protection Agency (EPA) and the World Health Organization (WHO) have set daily and weekly limits for safe mercury intake. Pregnant women, or women intending to become pregnant should minimize mercury intake from fish to avoid the possibility of birth defects.
A list of fish with their mercury concentration (in parts per million for a 3 oz serving) appears in Table 1 below.
Table 1: Mercury Content (parts per million) per 3 oz. serving
|Fish||Mercury Content||Fish||Mercury Content|
|Shrimp||ND||Canned tuna (light)||0.12|
|Salmon (fresh)||0.01||Mackerel (Spanish)||0.18|
|Flounder/Sole||0.05||Tuna (canned Albacore)||0.35|
ND = non detectable levels of mercury
Source: Levenson CW and Axelrad D. Too much of a good thing? Update on fish consumption and mercury exposure. Nutrition Rev (2006) 64: 139-145.
Lower numbers are better, indicating less mercury per 3 oz serving of fish. On a daily basis, males should stay at the 0.19 level or less; fish higher than this level can be eaten up to twice per week. Females should stay at a level of 0.14 or less for daily consumption and can go up to 0.38 twice per week. Orange roughy, a staple of some dieting bodybuilders, is far in excess of acceptable mercury levels for regular consumption.